Networking architectures typically have a layered design that more or less follows the International Standard Organization's Open System Interconnect (ISO/OSI) model. In this architecture it is difficult to pass information between layers that are not adjacent. In this respect, cross-layer Information Forwarding (IF) techniques are not common in today's networks. Generally, local solutions are provided to fulfil specific needs, which are typically focused on radio access; see, for example, the Voice over IP (VoIP) handling of 3rd Generation Partnership Project (3GPP) networks. However, for example for media delivery and adaptation, it is accepted, that cross-layer information can be desirable in the whole delivery chain in order to provide better Quality of Service (QoS) and user-perceived quality.
In this respect, in reference [A. Takács, F. Kalleitner, “Multimedia Transport Optimization through Forward Information Signalling”, PCT/EP2005/009387, August 2005, published as WO 2007/025560] it is described that, to build a media delivery framework that can utilize scalable media codecs for local adaptation requires intelligent adaptation functionalities, it is beneficial to provide detailed information about the media to be forwarded not only to the application layer, but to lower layers as well. This information allows e.g. the network layer to efficiently adapt to network congestions and the link and physical layers to apply efficient error protection schemes tailored for media delivery. Cross-layer communication appears to be the most appropriate way to distribute the above media information. It is beneficial for efficient media delivery to consider the properties of the networks and the applications together. In order to make an adaptation anywhere within the network, information must be provided about the feasible adaptation operations. This information is application and codec specific, and hence appropriate means for communication must be provided to permit application-aware adaptation of service delivery.
Currently, dedicated nodes with special functions are capable of supporting media stream adaptation. Translators, Mixers and Media Gateways (MGs) adapt the media traffic. E.g., for video stream adaptation a Media Aware Network Element (MANE) is defined [S. Wenger, M. M. Hannuksela, T. Stockhammer, M Westerlund, D. Singer, “RTP Payload Format for H.264 Video”, IEEE RFC 3984, February 2005]. The concept of a MANE goes beyond a normal functionality of a router or a gateway. That is, a MANE has to be aware of signalling. A MANE allows packet adaptation according to the needs of the media encoding format.
The MPEG-21 domain can be considered as a practical realization of the MANE concept. Within MPEG-21 more sophisticated adaptation methods are standardized than a simple End to End (E2E) feedback based adaptation. The main functionality of MPEG-21 domain is to deliver adapted content to the end user. The content adaptation must provide the best user perceived quality according to the physical constraints. These constraints are, e.g., terminal capabilities, network characteristics and user characteristics such as user interest or preference for a given media type. MPEG-21 uses an Adaptation Engine as logical unit to adapt the media content based on user and natural environment characteristics, terminal capabilities, and network characteristics. The Adaptation Engine operates on so-called Digital Items (DI). A DI contains the media itself and its metadata descriptor.
Real Time Protocol (RTP) session multiplexing and RTP Synchronization Source (SSRC) multiplexing [H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications”, IEEE RFC 3550, July 2003] are used to differentiate media layers produced by a single media source. In case of session multiplexing, each layer is associated with an individual RTP session. Each RTP session requires separate signalling, whereby each RTP session carries one RTP packet stream. In case of SSRC multiplexing, all layers are distributed in the same RTP session that comprises more than one RTP packet stream and each layer is identified by its SSRC. In both cases, the dependency of sessions must be signalled.
The applicant has identified the following problems with the existing solutions.
MANE: The main disadvantages of MANE are that it has to be aware of session control signalling and operates on application level. The nodes supporting MANE are rather complex, since transport and signalling interfaces must be supported or be controlled by external controllers. Moreover, the introduction of external controllers causes additional interfaces, adds processing and signalling delay and increases the maintenance cost.
MPEG-21: As MPEG-21 can be considered as a practical realization of MANE, thus MPEG-21 operates on application level as well. Moreover, for each MPEG-21 supporting node, the formulation of the adaptation decision must be repeated. Furthermore, the description of the adaptiveness of the media stream must be transferred (continuously) parallel to the media stream, which may result considerable overhead especially in case of voice transmission. Due to the centralized functions of MPEG-21, the scalability of the solution is low and the reaction time to altered channel conditions is relatively slow. In summary, this solution is rather complex.
RTP: There are two main functionalities to adapt media traffic, which can be applied at the borders of transport-level “clouds”. The first functionality (RTP Translator) is practically the similar transcoding procedure as it is realized by MPEG-21. The second functionality (RTP Mixer) could differentiate layers, however, the senders and the receivers do not have any control over the adaptation procedure, unless some mechanism is implemented to control this functionality.
The shortcomings of application layer driven media adaptation, as identified by the present applicant, can be summarized as follows:                Complex system architecture e.g. adaptation decision engine.        Increased bandwidth demands e.g. signalling of adaptiveness.        Increased end-to-end delay e.g. multiple adaptation decision and formulation steps.        
In addition to the list of references included at the end of the description, the following documents are also at least of background relevance: U.S. Pat. No. 5,940,610 and US 2002/0099842.